Zusammenfassung

Diel patterns in mobility and feeding behaviour of the larvae of the stream-dwelling trichopteran Sericostoma personatum larvae were investigated. Larvae fed at night on coarse particulate organic matter (CPOM) at the sediment surface. In the daytime they rested a few cm below the sediment surface, during which time their defaecation activity affected a release of fine particulate organic matter (FPOM) into the sediment. The amount of faeces (mean particle size = 0.1 ± 0.044 mm, x ± SD, n = 500) introduced into the sediment by the larvae, evaluated in two experiments, was 0.4-0.56 mg day-1. This amount did not differ significantly from the organic input resulting from bacterial activity (0.36-0.64 mg day-1). The presence of S. personatum larvae increased the sediment organic content by 42.9 mg (75.8%) and 59.8 mg (185.6%) AFDW per 16 cm3 sediment over a 90-day period, as compared with control systems containing no larvae.